The present invention pertains to the interconnection of switching offices for Common Channel Interoffice Signaling (CCIS) and more particularly to a single fault tolerant arrangement for CCIS printed wiring cards.
In present day electronic switching offices, a large percentage of the faults of printed wiring cards (PWCs) occur in the printed wiring cards, which provide power to other functional electronic printed wiring cards. Single faults in electronic PWCs, of a non-power supply nature, provide a less frequent source of faults. Switching offices have a reliability requirement due to the public policy of providing telephone service 24 hours a day on an uninterrupted basis.
A CCIS system is a switching office signaling arrangement connected between two offices for removing supervision and control signaling from voice trunks and transmitting this signaling between the switching offices via data links. As a result, more efficient use is made of the voice trunks. Each data link may control data transmission for 1000 to 2000 trunks. So, a single power failure may result in the loss of use of up to 2000 trunks. Some CCIS systems operate each particular data link with a separate power supply. This is a reliable configuration, but uneconomical approach.
An economical solution to this problem has been to provide a redundant pair of data link equipment which are powered separately. In this configuration, each power supply powers a large number of data link equipment. This is a viable solution, but not a reliable one because a single power supply failure may result in the loss of use of a large number of CCIS data links.
Therefore, it is the object of the present invention to provide an economical and reliable single fault tolerant CCIS data link arrangement for smaller switching offices.